Immutability specification and its applications

A location is said to be immutable if its value and thevalues of selected locations reachable from it are guaranteed toremain unchanged during a specified time interval. We introduce aframework for immutability specification, and discuss itsapplication to code optimization. Compared to a finaldeclaration, an immutability assertion in our framework can expressa richer set of immutability properties along three dimensions ---lifetime, reachability and context. We present a framework for processing and verifying immutabilityannotations in Java, as well as extending optimizations so as toexploit immutability information. Preliminary experimental resultsshow that a significant number (82%) of read accesses couldpotentially be classified as immutable in our framework. Further,use of immutability information yields substantial reductions (33%to 99%) in the number of dynamic read accesses, and also measurablespeedups in the range of 5% to 10% for certain benchmarkprograms.

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